1. Field of the Disclosure
The present application relates to the technical field of flow control components, and particularly to an electronic expansion valve.
2. Discussion of the Background Art
In the refrigerating and heating technical field, an electronic expansion valve is a refrigerant flow control component of refrigerating and heating devices, and the working process thereof is generally that: with a coil device power-on or power-off, a valve needle is driven to adjust an opening degree of a valve port so as to accurately adjust a flow of the refrigerant.
In some systems, when the electronic expansion valve is in a fully closed state and loses efficacy, or when a control system breaks down, if a compressor keeps running, a refrigerating circuit may be partially vacuumized and further the compressor and even the whole refrigerating system may be damaged. Therefore, a fully closed and flow allowed electronic expansion valve is gradually used to replace a fully closed and flow unallowed electronic expansion valve in these systems. The so-called “fully closed and flow allowed” means that when the valve port of the electronic expansion valve is closed by the valve needle of the electronic expansion valve, a certain flow is still allowed to pass, thereby effectively avoiding the problem caused by continuous running of the compressor that when the electronic expansion valve is in a fully closed state, the refrigerating system circuit is vacuumized.
In the conventional technology, the fully close and flow allowed electronic expansion valve generally adopts two types of structures: a grooving type and a gap type, which are described hereinafter respectively in conjunction with drawings.
Reference is made to FIGS. 1 and 2. FIG. 1 is a schematic view showing the structure of a valve needle cooperating with a valve port during a valve opening process of a grooving type electronic expansion valve in the conventional technology, and FIG. 2 is a flow curve to which the grooving type electronic expansion valve corresponds.
The so-called grooving type groove means that a groove is cut at a valve port portion of the electronic expansion valve to allow the seal of the valve port to be incomplete. Thus, when the electronic expansion valve is in the fully closed state, a portion between the valve needle and the valve port can not be completely sealed due to the existence of the groove, and there is still a small quantity of fluid flowing through the groove, thereby realizing the object that there is still some flow when the electronic expansion valve is fully closed.
A valve needle 18 is provided with a sealing conical surface 181 and an adjusting conical surface 182. The sealing conical surface 181 is configured to contact with a valve port 17 to realize a seal or a partial seal (FIG. 1 shows the grooving type electronic expansion valve and a valve port portion is provided with a groove to ensure a certain flow, thus the valve needle 18 can not completely seal the valve port). For avoiding the self-locking, a taper angle of the sealing conical surface 181 is generally set to be larger than 45 degrees. As shown in FIG. 1(a), for obtaining and setting a zero pulse flow valve, a pulse ranging from 0 to X1 is generally used to make the valve needle 18 to fully contact with the valve port 17. The valve needle is in the state of fully closing the valve port, the sealing conical surface 181 is in contact with the valve port 17, and a contacting portion is located on the sealing conical surface 181. A valve port plane P1 where the contacting portion is located is higher than a valve needle plane P2 where a boundary between the sealing conical surface 181 of the valve needle 18 and the adjusting conical surface 182 of the valve needle 18 is located (see an enlarged view of portion I). Thus, it could be understood from FIG. 2 that, a flow value of a 0˜X1 pulse section is the zero pulse flow value, and the zero pulse flow value is relevant to a depth of the groove. However, in the actual machining process of the groove, due to difference in hardness of materials and the difference of machining process, the depth of the groove cannot be ensured to be completely the same, and thus the zero pulse flow value can not be completely controlled. Furthermore, a width of the 0˜X1 pulse section is relevant to the debugging, an error in a debugging process may make X1 to fluctuate in a range and the error can generally reach 40 pulses, thus adversely affecting an adjusting accuracy of the electronic expansion valve.
Since the taper angle of the sealing conical surface 181 is different from a taper angle of the adjusting conical surface 182, flow change rates are different. During the valve opening process, before an inflection point passing the valve port, that is in a position corresponding to X2 pulse in FIG. 1, the valve port plane P1 where the contacting portion between the seal conical surface 181 and the valve port 17 is located is coincident with the valve needle plane P2 where the boundary between the seal conical surface 181 and the adjusting conical surface 182 is located, as shown in FIG. 1(b). With the valve needle 18 further moving upward, corresponding positions of the valve needle and the valve port at an X3 pulse are as shown in FIG. 1(c). At last, the valve port is in a fully opened state which is as shown in FIG. 1(d). The inflection point between X3 and X4 of the flow curve can be set according to the actual conditions.
According to the flow curve in FIG. 2, the flow change rate corresponding to the pulse section ranging from X1 to X2 is obviously larger than a flow change rate required by the electronic expansion valve, thus this pulse section can not be used in the practical application. Further, since X2 is relevant to X1, the value of X2 is undetermined. Consequently, the zero pulse flow value of the electronic expansion valve with such structure can not be accurately controlled, and due to the difference in valve opening pulse, the flow corresponding to a small opening degree section of 0˜X2, which is at a front end of the flow curve, has a low adjusting accuracy, thus the flow adjusting accuracy of the whole valve is low at a low pulse section. Furthermore, when the electronic expansion valve with such structure is in the fully closed state, the seal conical surface 181 is in contact with the valve port, thus an abrasion of the valve needle and the valve port is apt to occur when the electronic expansion valve is fully closed and just opened, and a phenomenon of valve sticking is likely to occur.
Reference is made to FIGS. 3 and 4. FIG. 3 is a structure schematic view showing that a valve needle cooperates with a valve port during a valve opening process of the gap type electronic expansion valve, and FIG. 4 is a flow curve to which the gap type electronic expansion valve corresponds.
The so-called “gap type” means that the valve needle of the electronic expansion valve is provided with an equal diameter section, and a diameter of the equal diameter section is smaller than that of the valve port, thus there is a certain gap when the valve needle cooperates with the valve port, thereby realizing an object that there is still some flow when the electronic expansion valve is fully closed.
A valve needle 19 includes an equal diameter section 191 and an adjusting section 192, the equal diameter section 191 has a cylinder shape, and a connecting position between the equal diameter section 191 and the adjusting section 192 is defined as a valve needle plane P3. A valve port 17 has the same structure as the valve port in the above grooving type electronic expansion valve, and a diameter of the valve port 17 is set to be larger than that of the equal diameter section 191. As shown in FIG. 3(a), when the electronic expansion valve is in the fully closed state, the valve needle plane P3 is lower than a valve port plane P4 where a top portion of the valve port located. There is a certain gap between the equal diameter section 191 and the valve port 17, a zero pulse flow value is ensured by controlling a size of the gap. Therefore, the requirement for the manufacture accuracy of the valve needle and the valve port having such a structure is high. Reference is made to FIG. 4, a position relationship between the valve needle and the valve port corresponding to the X1 pulse is as shown in FIG. 3(b). The valve needle plane P3 is coincident with the valve port plane P4. The width of the 0˜X1 pulse section is relevant to a debugging and a manufacture accuracy, and an error during the debugging process may make the X1 to fluctuate in a range and thus the X1 can not completely controlled. In the practical use, the flow value corresponding to 0˜X1 pulse keeps unchanged and a value of X1 is undetermined, therefore the 0˜X1 section pulse can not be used, thus causes an available pulse section to be decreased. FIGS. 3(c) and 3(d) respectively show the positions of the valve needle with respect to the valve port corresponding to X2 pulse and X3 pulse, and whether there is an inflection point between X2 and X3 of the flow curve or not can be determined according to the practical situation.
It can be seen that, for the fully closed and flow allowed electronic expansion valve in the conventional technology, no matter the grooving type or the gap type, both the zero pulse flows can not be easily and accurately controlled, and a pulse section having an unchanged flow value (a pulse section which can not be fully used) exists in the flow curve, thus a control accuracy of the electronic expansion valve is adversely affected to a certain extent.
Therefore, it is a technical problem urgently to be solved by those skilled in the art to design an electronic expansion valve, which can accurately control the zero pulse flow, allow the flow curve to be exclusive of a section having unchanged flow value, and fully use the small opening degree section of the electronic expansion valve.
Furthermore, under the affect of the design of flow channels inside the electronic expansion valve, a noise may be generated when a fluid passes through the valve port. Therefore, the flow channels of the electronic expansion valve should be specially designed for some middle-grade type and high-grade type machines.
Reference is made to FIG. 15, which is a schematic view showing the structure of a typical electronic expansion valve in the conventional technology.
The electronic expansion valve includes a valve seat 16. A first connecting pipe 14 and a second connecting pipe 15 are fixedly connected to the valve seat 16 respectively. The fluid enters the first connecting pipe 14, flows through a valve port 17′ arranged on the valve seat 16, and is discharged from the second connecting pipe 15 (the fluid may also enter the second connecting pipe 15 and be discharged from the first connecting pipe 14).
A housing 6 is fixedly connected to an upper side of the valve seat 16, the housing 6 is sealed by a cover 1, thus a sealed chamber is formed above the valve seat 16. A magnet rotor 8 and a lead screw 7 fixedly connected to the magnet rotor 8 are provided inside the housing 6. A valve needle 18′ is further arranged under the lead screw 7. The lead screw 7 cooperates with a nut 9 fixed on the valve seat 16 by a screw thread and can move relative to the nut 9. An electromagnetic coil (not shown in the figure) is sleeved on an outer end of the housing 6, the electromagnetic coil generates a pulse after being energized and drives the magnet rotor 8 to rotate, thus driving the lead screw 7 to rotate. Due to the screw thread fit, a rotating motion of the lead screw 7 is converted into upward and downward motion, which drives the valve needle 18′ connected to the lead screw 7 to move upward or downward to get close to or away from the valve port 17′ so as to change the opening degree of the valve port 17′ and realize the object of adjusting the flow.
For controlling a starting position and a stopping position of the upward and downward motion of the valve needle 18′, a stopping mechanism is further provided. The stopping mechanism includes a stopping rod 4 fixed on the lead screw and a stopping portion 2 fixed on the sealing cover 1. A helical spring guide rail 3 is fixed on the stopping portion 2, a sliding ring 5 is helically slidable on the helical guide rail 3, and one end of the sliding ring 5 abuts against the stopping rod 4 so as to realize the stopping object.
As shown in FIG. 16, a lower end portion of the valve port 17′ is provided with a flared opening 171′. Although the flared opening 171′ can reduce the noise to a certain degree, during the process that the fluid flows through the valve port 17′ from the first connecting pipe 14 and reaches the second connecting pipe 15, since an inner diameter of the valve port 17′ is much smaller than an inner diameter of the first connecting pipe 14, a flow area may still be suddenly changed when the fluid flows through the valve port 17′. Therefore, the fluid is apt to generate bubbles near the valve port 17′, and the bubbles are broken due to squeezing when passing through the valve port 17′, thus generating noise.
Therefore, it is a technical issue urgently to be addressed by those skilled in the art to design an electronic expansion valve which can further reduce the noise based on the conventional technology.